The present invention relates generally to optical switches and associated fabrication methods and, more particularly, to microelectromechanical single mode optical fiber cross-connect switch and associated fabrication methods.
Advances in thin film technology have enabled the development of sophisticated integrated circuits. This advanced semiconductor technology has also been leveraged to create MEMS (Micro Electro Mechanical System) structures. MEMS structures are typically capable of motion or applying force. Many different varieties of MEMS devices have been created, including microsensors, microgears, micromotors, and other microengineered devices. MEMS devices are being developed for a wide variety of applications because they provide the advantages of low cost, high reliability and extremely small size. In this capacity MEMS technology has been applied to the development of a free-space switch for single mode optical fibers.
Optical fiber offers many advantages compared with electric cables, including high bandwidth, low loss, lightweight, immunity from current surges and negligible electromagnetic interference. The use of extensive fiber optic networks are gaining wide acceptance and are being supported by the telecommunications industry as one of the international standards for high-speed local area networks (LANs). Fiber optic switches are used in the networks to reconfigure the network and/or increase overall reliability. For example, optical bypass switches have been employed to bypass failed nodes within the network.
The fiber optic switches can be fabricated using either a free-space approach or a waveguide approach. The free-space approach offers a number of advantages over the conventional waveguide approach. For an example of a conventional waveguide approach see the technical publication by L. A. Field et al., entitled xe2x80x9cMicromachined 1xc3x972 Optical-Fiber Switchxe2x80x9d International Solid-State Sensors and Actuators Conferencexe2x80x94Transducers 1995, Stockholm, Sweden Jun. 25-29, 1995. The free space approach has lower coupling loss and minimal cross talk. However, conventional free-space fiber optic switches employ bulk optical elements and are typically very costly to manufacture. MEMS technology allows for improved performance of free space fiber optic switches and can be manufactured at relatively minimal cost. For examples of such free space MEMS switches see the technical publications by H. Toshiyoshi et al., entitled xe2x80x9cOptical Crossconnection by Silicon Micromachined Torsion Mirrorsxe2x80x9d, Digest IEEE/LEOS 1996 Summer Topical Meetings, pp. 63-64, Keystone, CO, Aug. 5-9, 1996 and C. Marser et al., entitled xe2x80x9cVertical Mirrors Fabricated by Reactive Ion Etching for fiber Optical Switching Applicationsxe2x80x9d, Tenth IEEE International MEMS Workshop, pp. 349-354, 1997.
In the most rudimentary form, the MEMS fiber optical switch is capable of routing input from a single fiber to one of two possible output fibers. The fiber-based telecommunications industry desires a microelectronic switch architecture that will permit the integration of multiple switch elements into an array. A critical aspect of the array design is the ability to create a non-blocking, one-to-one operable switch array, such that, setting one switch element to route one input fiber will not interfere with the setting of other switch elements intended to route other input fibers. Of additional importance is the desire to create an array architecture that is scaleable, allowing. for numerous input fibers to be routed to output fibers as dictated by the application. The fiber optical switch must be designed to limit insertion loss by providing for a stationary reflective state that allows for optical fibers to be redirected in a reliable fashion.
Another concern of current microelectronic optical switches is the ability to properly actuate the reflective structure, or mirror, from a non-reflective state to a reflective state. The use of magnetic fields to actuate the mirrors has provided marginal success. In most instances, a constant magnetic field is used that provides maximum torque to the mirror at the midway point between the non-reflective and reflective state. Once the torque peaks at the midway point it gradually decreases until it approaches low torque as the mirror reaches the reflective state. The low torque effect impedes the mirror from consistently attaining the requisite reflective state.
Therefore, while some free space optical fiber cross-connect switches have been developed, it would still be advantageous to develop other types of optical cross-connect switches that would operate more reliably in terms of minimizing insertion loss, allow for a non-blocking, one-to-one operable switch matrix, provide for a scaleable array of switches, allow for consistent actuation and lend themselves to cost-effective manufacturing. Consequently, these MEMS optical cross-connect switches would be suitable for a wider variety of telecommunications applications. Numerous telecommunications applications, such as fiber optic networks, would benefit from MEMS optical cross-connect switches having these improved attributes.
The present invention provides for a microelectromechanical structure capable of switching optical fibers from an input fiber to one of two or more output fibers. In one embodiment, the MEMS optical cross-connect switch comprises a first microelectronic substrate having a pop-up mirror disposed on the surface of the substrate and a rotational magnetic field source disposed proximate the first substrate that provides the actuation force to the pop-up mirror. The rotational magnetic field may comprise a variably controlled magnetic field capable of maximizing torque throughout the actuation period. The variably controlled magnetic field may comprise a pair of wire coils having generally orthogonal magnetic field axis. The variably controlled magnetic field source can be adjusted during actuation by varying the current supplied to the coil(s) thereby maximizing the magnetic torque and generating optimal actuation force throughout the movement of the pop-up mirror from the non-reflective to reflective state, Additionally, a magnetic pole piece may be positioned proximate the second microelectronic substrate to provide further magnetic attraction to the pop-up mirror.
Additionally, this embodiment may comprise at least one positioning structure disposed so as to act as a stop-gate for positioning the pop-up mirror in a reflective state. The positioning structure may comprise a pillar-like structure extending from a second microelectronic substrate that is in a fixed positional relationship relative to the first microelectronic substrate. The positioning structure may be electrostatically activated through a voltage source connected to the second substrate such that electrostatic activation of the positioning structure causes the pop-up mirror to be xe2x80x9clockedxe2x80x9d in the xe2x80x9cuprightxe2x80x9d, reflective state. In addition, the MEMS optical cross-connect. switch of this embodiment may comprise a tether device that may be electrostatically activated through connection to the first substrate to provide a xe2x80x9cclamp-downxe2x80x9d voltage to the pop-up mirror in the pop-up mirror""s prone, non-reflective state.
In another embodiment of the present invention the MEMS optical cross-connect switch comprises a first microelectronic substrate having a pop-up mirror disposed on the surface of the substrate and a positioning structure disposed in a fixed positional relationship relative to the first microelectronic substrate. The positioning structure serves to position the pop-up mirror when the mirror has been actuated to a reflective state. The positioning structure may comprise a pillar-like structure extending from a second microelectronic substrate that is in a fixed positional relationship relative to the first microelectronic substrate. The positioning structure may be electrostatically activated through a voltage source connected to the second substrate such that electrostatic activation of the positioning structure causes the pop-up mirror to be xe2x80x9clockedxe2x80x9d in the xe2x80x9cuprightxe2x80x9d, reflective state. The actuation mechanism for this embodiment may comprise a magnetic field source. Additionally, the magnetic field source may be a rotational magnetic field source having the capability to be variably controlled. Additionally, a magnetic pole piece may be positioned within or proximate the second microelectronic substrate to assure that the pop-up mirror has sufficient magnetic torque to allow for the mirror to reach the desired fully xe2x80x9cuprightxe2x80x9d, reflective state.
In yet another embodiment of the present invention, a method for cross-connect switching of optical signals in a microelectronic device comprises the steps of receiving an input signal on an optical path, generating a rotational magnetic field to actuate a pop-up mirror from a non-reflective state to a reflective state and reflecting the input signal off the pop-up mirror on another optical path. Additionally, the method may comprise maintaining position of the pop-up mirror in the reflective state by restricting movement of the pop-mirror with a positioning structure. An alternate step may comprise clamping electrostatically the pop-up mirror in a reflective state by applying voltage to the associated positioning structure.
An additional method for cross-connect switching of optical signals in a microelectronic device comprises the steps of receiving an input signal on an optical path, actuating magnetically a pop-up mirror from a non-reflective state to a reflective state, maintaining positioning of the pop-up mirror at a reflective position and reflecting the input signal off the pop-up mirror on another optical path. The step of maintaining positioning may further comprise restricting the actuation of the pop-up mirror with at least one positioning structure, such as a positioning structure extending from a microelectronic substrate. The step of actuating magnetically may comprise generating a rotational magnetic field to actuate the pop-up mirror from a non-reflective state to a reflective state.
Additionally, the present invention is embodied in an optical cross-connect switch array that comprises a first microelectronic substrate having at least two pop-up mirrors disposed on the surface of the first substrate and a rotational magnetic field source disposed proximate the first microelectronic substrate. The cross-connect switch array may comprise at least two positioning structures disposed in a fixed positional relationship relative to the first microelectronic substrate so as to serve to position the pop-up mirror in a reflective state. The positioning structures may comprise pillar-like structures extending from a second microelectronic substrate that is held in a fixed positional relationship relative to the first microelectronic substrate. Typically, the array will comprise n columns and m rows of pop-up mirrors and corresponding positioning structures aligned so as to allow for a non-blocking, one-to-one switching matrix.
In yet another embodiment of the present invention, an optical cross-connect switch array may comprise a first microelectronic substrate having at least two pop-up mirrors disposed on the surface of the first substrate and a second microelectronic substrate disposed in a fixed positional relationship relative to the first microelectronic substrate. The second microelectronic substrate having at least two positioning structures extending therefrom towards the first microelectronic substrate. The positioning structures serve to restrict further movement of the pop-up mirror beyond the position of the reflective state. The pop-up mirrors of the array may be actuated by a magnetic field source, such as a rotational magnetic field source. Typically, the array will comprise n columns and m rows of pop-up mirrors and corresponding positioning structures aligned so as to allow for a non-blocking, one-to-one switching matrix.
In yet another embodiment of the present invention, an optical cross-connect switch array may comprise a first microelectronic substrate having at least two pop-up mirrors disposed on the surface of the first substrate and a second microelectronic substrate disposed in a fixed positional relationship relative to the first microelectronic substrate. Additionally this embodiment includes a magnetic field source that provides for a magnetic field oriented with respect to the first microelectronic substrate to interact with the at least two pop-up mirrors and at least two magnetic pole pieces disposed proximate to the second microelectronic substrate to provide for further magnetic attraction of the pop-up mirror.
The present invention is also embodied in a MEMS optical cross-connect switching system having a first microelectronic substrate, at least one optical fiber input and two optical fiber outputs disposed about the perimeter of the first microelectronic substrate, at least one pop-up mirror disposed proximate the first microelectronic substrate and a rotational magnetic field source that actuates the pop-up mirrors from a non-reflective state to a reflective state. An optional MEMS optical cross-connect switching system may comprise a first microelectronic substrate, at least one optical fiber input and two optical fiber outputs disposed about the perimeter of the first microelectronic substrate, at least one pop-up mirror disposed proximate the first microelectronic substrate and a second microelectronic substrate disposed in a fixed positional relationship relative to the first microelectronic substrate. The second microelectronic substrate having at least one positioning structure extending therefrom towards the first microelectronic substrate. The positioning structure serves to restrict further movement of the pop-up mirror beyond the position of the reflective state.
The MEMS optical cross connect switch of the present invention benefits from having a rotational magnetic field source that serves as the mechanism for actuation. In this fashion, the pop-up mirrors can be fully and repetitiously actuated from non-reflective state to reflective state. Additionally, the invention provides for the use of magnetic pole pieces as an alternative option to fully and repetitiously actuate the pop-up mirror from a non-reflective state to a reflective state. In another embodiment, the present invention employs positioning structures, such as pillar-like structures, that serve as stop-gates for the pop-up mirrors as they reach their respective reflective states. Moreover, the pop-up mirrors can be xe2x80x9clocked-inxe2x80x9d to the reflective state by applying electrostatic voltage across the positioning structures. The unique design of the positioning structures allows for a switch array to be configured that provides for a non-blocking, one-to-one operable switch array, such that, setting one switch element to route one input fiber will not interfere with the setting of other switch elements intended to route other input fibers. Also, the present invention provides for scaleable array architecture thus, allowing for numerous input fibers to be routed to output fibers as dictated by the application. The free-space, MEMS technology Fiber optical switch of the present invention limits insertion loss by providing for a stationary reflective state that allows for optical fibers to be redirected in a reliable fashion.